3 Answers
3

The helmet itself is (probably) polysterene foam inner and a harder plastic shell, it's fine to wash this in water and some mild detergent (eg dish soap)

You can try and wash the straps in hot soapy water.

The problem is the pads. Usually washing the pads means that they come unglued, the surface layers separate from the inner cushion part. All you can do is keep the extra ones you get to size a new helmet and swap them.

I don't know if pro racing type helmets come with multiple sets of replaceable straps and pads - but they should.

You should be able to wash, even submerge, your helmet in water, with perhaps a dash of mild detergent. Use no other solvents or additives. If submerging, agitate very slowly, since the force of water against pads or other loosely-attached elements can be quite strong.

Dry by draining thoroughly and placing in a slightly warm place (not somewhere where you could not sit comfortably for at least a few minutes -- high heat can kill a helmet). Expect it to take 2-3 days to completely dry if submerged. DO NOT put the helmet "away" (in a bag or box, in an enclosed area, etc) before it is thoroughly dry.

If pads are removable, remove them and wash separately, but washing with the helmet should not harm the pads (or their adhesive) any more than riding in the rain or sweating in the helmet.